The disclosure of Japanese Patent Application No. 2001-006528 filed on Jan. 15, 2001, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an internal combustion engine that performs an automatic stop/start control of a vehicular internal combustion engine and, more particularly, to an internal combustion engine control apparatus that permits the aforementioned automatic stop if the temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner is higher than a threshold, and prohibits the automatic stop/start if the temperature of the cooling medium is lower than the threshold.
2. Description of Related Art
Automatic air-conditioners for cabin air-conditioning in motor vehicles are known. The automatic air-conditioner is an apparatus that automatically maintains a set temperature in the cabin. The apparatus detects an outside air temperature and a cabin temperature using temperature sensors, and adjusts the blow-off air temperature and the air flow through the processing by an electronic control unit, thereby maintaining an appropriate air-conditioned state in the cabin. The automatic air-conditioner, when heating, efficiently uses heat from the cooling water of the internal combustion engine so as to adjust the blow-off air temperature and thereby maintain a comfortable room temperature in the cabin (Japanese Patent Application Laid-Open Publication No. 5-221233).
For improvements in fuel economy, there exist vehicles equipped with a generally-termed economy-running (hereinafter, referred to as xe2x80x9ceco-runxe2x80x9d) system, that is, an automatic stop/start system capable of automatically stopping the internal combustion engine when the vehicle has stopped running at an intersection or the like, and allowing the vehicle to launch through automatic start-up of the engine achieved by operating a motor-generator or the like at the time of a launching operation performed by a driver. If an automatic air-conditioner is used in such a vehicle, the heating utilizing the cooling water of the internal combustion engine may become impossible due to a drop in the cooling water temperature during an automatic stop of the engine. To avoid this situation, a control of prohibiting the automatic stop of the internal combustion engine and starting the internal combustion engine is performed in some cases.
For example, a threshold value of cooling water temperature is provided. If the cooling water temperature is above the threshold value, the automatic stop of the internal combustion engine is permitted. If the cooling water temperature becomes lower than the threshold value, the automatic stop of the internal combustion engine is prohibited and the engine is started. If in this case, the required blow-off air temperature of the automatic air-conditioner is relatively low, no heating problem occurs despite a reduced cooling water temperature during a stop of the internal combustion engine. Conversely, if the required blow-off air temperature of the automatic air-conditioner is relatively high, a drop in the cooling water temperature will likely make it impossible to maintain a requested heating. Therefore, if the required blow-off air temperature is higher, the threshold value is raised so that if the cooling water temperature decreases, operation of the internal combustion engine is resumed at an early stage of the decrease in cooling water temperature, whereby the cooling water temperature is kept relatively high. In this fashion, control is performed so that the sufficient heating by the automatic air-conditioner is possible over a broad range.
At the time of transition of the cooling water temperature caused by discontinuation or start of generation of heat by the internal combustion engine due to, for example, an automatic stop or an automatic startup of the engine, the cabin temperature changes with a delay from the change in the cooling water temperature. Due to this delay, after the engine has been stopped through the automatic stop, there exists a period during which the cabin heating using the cooling water whose temperature is decreasing can be continued without any problem in the cabin comfort. According to the related-art technology, however, the automatic stop of the internal combustion engine is prohibited and operation of the engine is restarted when the cooling water temperature decreases to a threshold value (which may include a hysteresis width set so as to prevent hunting in control) that is the same as the threshold value used for the increasing cooling water temperature. Thus, the automatic stop of the internal combustion engine is ended when there still is no heating problem. This indicates that the use of a threshold as in the related-art technology does not allow full exploitation of the fuel economy improvement advantage of the automatic stop.
In a region of low blow-off air temperatures, the threshold value is set low. A reduced threshold value increases the length of time consumed for the cooling water temperature to reach the threshold value if the internal combustion engine is automatically stopped. Therefore, in that case, the automatic stop state can be maintained for a long time, and therefore, fuel economy can be sufficiently improved. Conversely, in a region of high blow-off air temperatures, the threshold value is set high due to the need for sufficiently high blow-off air temperature. Therefore, if the internal combustion engine is automatically stopped, the cooling water temperature soon reaches the threshold value, and therefore, the automatic stop ends in a short time. However, it has been found that if the cooling water temperature decreases when the required blow-off air temperature is within a high temperature region, the cabin comfort can be retained for a relatively long time despite decreasing cooling water temperature since the internal combustion engine is automatically stopped while the cabin temperature is sufficiently high. Thus, the related-art technology ends the automatic stop in a short time although the comfort of air-conditioning can be retained for a relatively long time following an automatic stop of the internal combustion engine. The related-art technology cannot be said to achieve sufficient improvement in fuel economy.
It is an object of the invention to increase the duration of the automatic stop of the internal combustion engine and therefore enhance the fuel economy improving effect by reducing the region of prohibiting the automatic stop of the internal combustion engine corresponding to the air-conditioned state in the cabin.
Means for achieving the aforementioned object and the operation and advantages thereof will be described below.
A vehicular internal combustion engine control apparatus according to a first aspect of the invention includes: engine automatic stop-startup means for automatically stopping the internal combustion engine if a state of operation of the internal combustion engine satisfies an automatic stop condition, and for automatically starting the internal combustion engine if the state of operation of the internal combustion engine satisfies an automatic startup condition; and engine automatic stop permission-prohibition means for permitting an automatic stop of the internal combustion engine if a temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner is higher than a threshold value, and for prohibiting the automatic stop if the temperature of the cooling medium is lower than the threshold value. The control apparatus is characterized in that the threshold value related to the engine automatic stop permission-prohibition means is variable in accordance with at least one of an inside-cabin temperature and values related to the inside-cabin temperature, and that a hysteresis width of the threshold value is set greater than a hysteresis width that is needed to prevent hunting in control.
Since the hysteresis width of the threshold value is set greater than a hysteresis width that is needed to prevent hunting in control, the threshold value for the time of decrease in the engine cooling water temperature can be set at a sufficiently low temperature side, in comparison with the threshold value for the time of increase in the engine cooling water temperature. That is, at the time of decrease in the engine cooling water temperature, the inside-cabin temperature or a value related to the inside-cabin temperature is in a state corresponding to an engine cooling water temperature that is higher than the present engine cooling water temperature due to a delay during a transitional period. Therefore, the threshold value for the time of decrease in the engine cooling water temperature can be set even lower than a threshold value that is conceived factoring in the hunting in control with respect to the threshold value for the time of increase in the engine cooling water temperature.
Since the threshold value for the time of decrease in the engine cooling water temperature can be set sufficiently low, the internal combustion engine automatic stop prohibition region can be reduced. Hence, the automatically stopped state of the internal combustion engine can be maintained for an increased length of time, thereby enhancing the fuel economy improvement advantage.
A vehicular internal combustion engine control apparatus according to a second aspect of the invention includes: engine automatic stop-startup means for automatically stopping the internal combustion engine if a state of operation of the internal combustion engine satisfies an automatic stop condition, and for automatically starting the internal combustion engine if the state of operation of the internal combustion engine satisfies an automatic startup condition; and engine automatic stop permission-prohibition means for permitting an automatic stop of the internal combustion engine if a temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner is higher than a threshold value, and for prohibiting the automatic stop if the temperature of the cooling medium is lower than the threshold value. The control apparatus is characterized in that the threshold value related to the engine automatic stop permission-prohibition means and a hysteresis width of the threshold value are variable in accordance with an inside-cabin temperature or a value related to the inside-cabin temperature.
Since the threshold value related to the engine automatic stop permission-prohibition means and the hysteresis width of the threshold value are variable in accordance with the inside-cabin temperature or a value related to the inside-cabin temperature, a portion of the threshold value lower than a fixed threshold value can be set by changing the threshold value in correspondence to the inside-cabin temperature or the value related to the inside-cabin temperature. Therefore, the internal combustion engine automatic stop prohibition region can be reduced, and the automatically stopped state of the engine can be maintained for an increased length of time. Hence, the fuel economy improvement advantage can be enhanced.
In addition, the hysteresis width may be expanded in accordance with the inside-cabin temperature or a value related to the inside-cabin temperature. Particularly in a region where the inside-cabin temperature or the value related to the inside-cabin temperature is high, the threshold value for the case of decreasing engine cooling water temperature can be set low. Therefore, particularly in the region where the inside-cabin temperature or the value related to the inside-cabin temperature is high, the internal combustion engine automatic stop prohibition region can be reduced. Hence, the automatically stopped state of the internal combustion engine can be maintained for a long time, and the fuel economy improvement advantage can be enhanced.
In the internal combustion engine control apparatus according to the second aspect of the invention, it is preferable that the hysteresis width be set greater than a hysteresis width that is needed to prevent hunting in control.
Since the hysteresis width of the threshold value is set greater than a hysteresis width that is needed to prevent hunting in control, the threshold value for the time of decrease in the engine cooling water temperature can be set sufficiently lower than the threshold value for the time of increase in the engine cooling water temperature. That is, at the time of decrease in the engine cooling water temperature, the inside-cabin temperature or a value related to the inside-cabin temperature corresponds to an engine cooling water temperature that is higher than the present engine cooling water temperature due to a delay during a transitional period. Therefore, the threshold value for the time of decrease in the engine cooling water temperature can be set even lower than a threshold value that is conceived factoring in the hunting in control with respect to the threshold value for the time of increase in the engine cooling water temperature.
By setting the threshold value for the time of decrease in the engine cooling water temperature at a sufficiently low level, the internal combustion engine automatic stop prohibition region can be further reduced. Hence, the automatically stopped state of the internal combustion engine can be maintained for an increased length of time, thereby enhancing the fuel economy improvement advantage.
In any one of the foregoing constructions, it is preferable that the hysteresis width be set in such a range that a cabin comfort is not degraded if the temperature of the cooling medium decreases from a state where the automatic stop is permitted by the engine automatic stop permission-prohibition means.
Therefore, since the hysteresis width is set in such a range that a cabin comfort is not degraded if the temperature of the cooling medium decreases, it is possible to sufficiently reduce the internal combustion engine automatic stop prohibition region and sufficiently enhance the fuel economy improvement advantage without discomforting an occupant in terms of air-conditioning.
In any one of the above-described constructions, it is preferable that the threshold value related to the engine automatic stop permission-prohibition means be variable in accordance with a needed blow-off temperature provided at a time of automatic air-conditioning of the cabin air-conditioner which is a value related to the inside-cabin temperature, and that the threshold value rise as the needed blow-off temperature rises.
More specifically, the threshold value may be variable in accordance with a needed blow-off temperature provided at a time of automatic air-conditioning of the cabin air-conditioner, and may be set so as to rise as the needed blow-off temperature rises.
Therefore, in the case where the needed blow-off temperature for the time of automatic air-conditioning is set low in accordance with the outside air temperature or an occupant""s request, it is possible to maintain the automatically stopped state for a long time without adverse effect on air-conditioning, and enhance the fuel economy improvement advantage, in comparison with the case where the needed blow-off temperature is high. In the case where the needed blow-off temperature is set high, the automatically stopped state can be prohibited at a relatively early stage, and therefore, adverse effect on air-conditioning can be avoided, in comparison with the case where the needed blow-off temperature is low. Furthermore, in the case where the needed blow-off temperature is set high, too, the threshold value for the time of decrease in the engine cooling water temperature can be set sufficiently low, and the internal combustion engine automatic stop prohibition region can be reduced, so that the automatically stopped state of the internal combustion engine can be maintained for an increased time. Therefore, the fuel economy improvement advantage can be further enhanced.
In the above-described construction, the threshold value may be reduced for correction as an outside-cabin air temperature or an inside-cabin air temperature rises. Furthermore, the hysteresis width of the threshold value may be expanded as an outside-cabin air temperature or an inside-cabin air temperature rises. In this case, it is also preferable to expand the hysteresis width of the threshold value toward a low temperature side.
In the above-described construction, it is preferable that the hysteresis width of the threshold value related to the engine automatic stop permission-prohibition means increase as the needed blow-off temperature rises.
The degree of delay of decrease in the inside-cabin temperature with respect to decrease in the engine cooling water temperature is greater if the needed blow-off temperature is higher. That is, in the case where the needed blow-off temperature is relatively high, air-conditioning comfort is more likely to be maintained despite a decrease in the engine cooling water temperature, and therefore the hysteresis width can be set greater than in the case where the needed blow-off temperature is relatively low. Therefore, the automatically stopped state of the internal combustion engine can be maintained for an increased length of time, and the fuel economy improvement advantage can be further enhanced.
In the above-described construction, it is preferable that the threshold value related to the engine automatic stop permission-prohibition means be variable in accordance with the inside-cabin temperature, and that the threshold value decrease as the inside-cabin temperature rises.
More specifically, the threshold value is variable in accordance with the inside-cabin temperature, is set so as to decrease as the inside-cabin temperature rises. In the case where the inside-cabin temperature is relatively high, the degree of delay of degradation in the air-conditioning comfort with respect to decrease in the engine cooling water temperature is greater and therefore the threshold value can be set lower, in comparison with the case where the inside-cabin temperature is relatively low. Therefore, the automatically stopped state of the internal combustion engine can be maintained for an increased length of time, and the fuel economy improvement advantage can be further enhanced.
Furthermore, the hysteresis width of the threshold value may be expanded toward a low temperature side as the needed blow-off temperature rises.
In the above-described construction, it is preferable that the hysteresis width of the threshold value related to the engine automatic stop permission-prohibition means be variable in accordance with an outside-cabin air temperature which is a value related to the inside-cabin temperature, and that the hysteresis width increase as the outside-cabin air temperature rises.
More specifically, the hysteresis width of the threshold value is variable in accordance with the outside-cabin air temperature, and is set so as to decrease as the outside-cabin air temperature rises. In the case where the outside-cabin air temperature is relatively high, the degree of delay of degradation in the air-conditioning comfort with respect to decrease in the engine cooling water temperature is less and therefore the hysteresis width can be set greater, in comparison with the case where the outside-cabin air temperature is relatively low. Therefore, the automatically stopped state of the internal combustion engine can be maintained for an increased length of time, and the fuel economy improvement advantage can be further enhanced.
An internal combustion engine control apparatus in accordance with a third aspect of the invention includes: engine automatic stop-startup means for automatically stopping the internal combustion engine if a state of operation of the internal combustion engine satisfies an automatic stop condition, and for automatically starting the internal combustion engine if the state of operation of the internal combustion engine satisfies an automatic startup condition; and engine automatic stop permission-prohibition means for permitting an automatic stop of the internal combustion engine if a temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner is higher than a threshold value, and for prohibiting the automatic stop if the temperature of the cooling medium is lower than the threshold value. The control apparatus is characterized in that the threshold value is variable in accordance with a first value selected from an inside-cabin temperature and values related to the inside-cabin temperature, and that the threshold value is increase-decrease corrected in accordance with a second value that is different from the first value and that is selected from the inside-cabin temperature and the values related to the inside-cabin temperature.
Thus, the threshold value related to the engine automatic stop permission-prohibition means is variable in accordance with the first value selected from the group consisting of the inside-cabin temperature and values related to the inside-cabin temperature. Therefore, the threshold value can be set sufficiently low in accordance with a situation of air-conditioning indicated by the first value. For example, the threshold value can be set low in the case of a decrease in the engine cooling water temperature depending on the state of the first value. Therefore, the internal combustion engine automatic stop prohibition region can be reduced.
Furthermore, the threshold value is increase-decrease corrected in accordance with a second value that is different from the first value and that is selected from the group consisting of the inside-cabin temperature and the values related to the inside-cabin temperature. In this case, the threshold value can be set further low in accordance with a situation of air-conditioning indicated by the second value. Therefore, the internal combustion engine automatic stop prohibition region can be sufficiently reduced. Hence, the automatically stopped state of the internal combustion engine can be maintained for a long time, and the fuel economy improvement advantage can be further enhanced.
In the above-described construction, it is preferable that the first value be the inside-cabin temperature, and the second value be an outside-cabin air temperature.
More specifically, the inside-cabin temperature may be adopted as the first value, and the threshold value may be variable in accordance with the inside-cabin temperature. The outside-cabin air temperature may be adopted as the second value, and the threshold value may be increased or decreased for correction in accordance with the outside-cabin air temperature.
At a high inside-cabin temperature side, the threshold value may be set low if the engine cooling water temperature decreases. Therefore, particularly in a region where the inside-cabin temperature is high, the internal combustion engine automatic stop prohibition region can be reduced. Furthermore, at a high outside-cabin air temperature side, the threshold value can be corrected so as to reduce. Therefore, particularly in a region where the outside-cabin air temperature is high, the internal combustion engine automatic stop prohibition region can be further reduced.
Hence, the automatically stopped state of the internal combustion engine can be maintained for a long time, and the fuel economy improvement advantage can be further enhanced.
In addition to the above-described construction, the invention further includes the following constructions.
(i) An internal combustion engine control apparatus which executes an automatic stop-startup mode of automatically stopping a vehicular internal combustion engine if a state of operation of the internal combustion engine satisfies an automatic stop condition, and of automatically starting the internal combustion engine if the state of operation of the internal combustion engine satisfies an automatic startup condition, and which executes prohibition of the automatic stop-startup mode in accordance with decrease in the temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner, the control apparatus being characterized in that a range for execution of the automatic stop-startup mode is set in such a range that a cabin temperature comfort is not degraded if the temperature of the cooling medium decreases.
(ii) An internal combustion engine control apparatus which executes an automatic stop-startup mode of automatically stopping a vehicular internal combustion engine if a state of operation of the internal combustion engine satisfies an automatic stop condition, and of automatically starting the internal combustion engine if the state of operation of the internal combustion engine satisfies an automatic startup condition, and which executes prohibition of the automatic stop-startup mode in accordance with decrease in the temperature of a cooling medium of the internal combustion engine used as an air-conditioning heat source by a cabin air-conditioner, the control apparatus being characterized in that a range for execution of the automatic stop-startup mode is set in such a range that a cabin temperature comfort is not degraded in accordance with an air-conditioning situation if the temperature of the cooling medium decreases.